Method and apparatus for coating paper



Jan. 7, 1941. L. J. GOLD METHOD AND APPARATUS FOR COATING PAPER FiledJuly 24, 1957 L s 0 Y may xm W m N 0 m E Patented Jan. 7, 1941 UNITEDSTATES PATENT OFFICE Leon .l. Gold, Brooklyn, N. Y., assignor toPlastics Finishing Corporation, Brooklyn, N. Y., a corporation of NewYork Application July 24, 1937, Serial No. 155,294

Claims. (01. 91-55) This invention relates to the preparation ofdecorative and protective surface coatings on sheet or strip material,It provides an improved method and apparatus which combine withsimplicity and economy of operation the capacity to produce, by a singledirect application of liquid coating material, lacquer coatings that arepermanently bonded to paper or like materials and possess highlydesirable surface characteristics. 10 Prior to my invention printed andlithographed paper for advertising purposes and the like has beenprepared with a coating of transparent lacquer, usually a cellulosicmaterial such as cellu-; lose acetate, either by producing a thin sheetof the coating material and then sealing it to the paper or by applyinga film of the'coating material while in a liquid state. The formerpractice results in coated paper of excellent appearance, but it isexpensive and a tendency for the coating to split away from the paper isencountered which causes considerable difficulty. The practice ofapplying a film of liquid coating material to the paper is economicaland the dried coating does not peel off from the paper, but unlessseveral films of the material are applied separately to the paper theappearance and value of the final product are inferior when usualcoating methods are used, due to non-uniformities in the surface of thecoating which greatly reduce its gloss and reflective power, This ispartly attributable to absorption of a large part of a single film ofcoating material by the paper. I have found that the inferior quality ofthe prior product is also caused by the liquid applying roller and thefeed rollers of higher peripheral speed which are used in the usualmethod.

One of the objects of my invention is to provide a new method, togetherwith apparatus for practicing it, which enable the economicalproduction, by a single application of liquid coating material, ofimproved lacquer coated sheet material having a glossy appearanceclosely similar to that of the laminated constructions referred toabove.

Another object of the invention is to provide a method and apparatuswhich are capable of continuous operation on very long strips of thesheet material to be coated and which produce coatings of uniform highsurface gloss throughout the length of the strips.

Another object isto provide a method and apparatus of the type abovementioned which are adapted to withstand long periods of continuous usewithout adding to the bulkiness of the apparatus and in which partsultimately requiring attention due to accumulation of coating materialthereon may be replaced without substantial interruptlons in operation.

Still another object of the invention is to provide a method for coatingpaper with liquid lacquer or varnish which safeguards the coatingagainst surface contamination from the time it is applied until aproduct having a dry glossy surface and no longer susceptible ofcontamination is obtained.

Another object of the invention is to provide a method of coating whichattains the objects mentioned above and at the same time producesembossed or engraved indicia or designs on the coated surface.

I have found that the foregoing and other desirable objectives may beaccomplished by applying a single film of liquid coating material to astrip of paper or other sheet material undergoing treatment, coveringthe coating shortly after it is applied and while it is still moist witha band of flexible sheet-like material having a smooth polished surfaceadjacent the coating, pressing the coated strip and the band together sothat the smooth surface of the latter is brought into intimate contactwith and molds the surface of the moist film of coating material,maintaining this intimate contact until the coating material has driedand then separating the band from the dried coated strip. In carryingout these operations of the improved method a strip or successive stripsof the paper or other similar material to be coated are movedcontinuously past coating applying means, such as a roller dipping intoa bath of the coating material, in order continuously to apply a film ofthe liquid coating material to one face of the paper. A band of flexiblesheet-like material of a width sufficient to cover the coated por tionof the paper strip is maintained in condition for use, for example on asuitable reel, so that it may be brought into face-to-face contact withthe coated strip as the latter moves away from the applying means. Thecovering band is moved at the same speed as the coated strip, and afterthe strip and band have been brought into contact they are continuouslypassed together through pressure applying means which forces the smoothsurface of the flexible band into intimate contact with the moistcoating and thereby spreads the coating uniformly on the strip andimparts to the surface of the coating a smoothness or polish similar tothat existing on the adjacent surface of the band. From the pressureapplying means the combined materials are passed through a drying Cl u Iknown examples.

zone, which may include a heating and drying chamber or may consistmerely of a zone in which the materials are kept; together for anydesired length of time until the coating has become thoroughly dry.Thereafter, the covering band of flexible material is stripped from thecoated paper, and a product of high quality is obtained which possessesa uniform coating having a very smooth glossy surface.

The improved method may be used in preparing coatings of various kindsof lacquers and varnishes. It is of particular value for the productionof paper coated with transparent cellulosicmaterials such as celluloseesters and ethers,

of which cellulose acetate and pyroxylin are well Printed andlithographed paper having a decorative and protective coating ofcellulose acetate has a wide field of use for advertising purposes andthe like. The method and apparatus of my invention produce paper of thistype which is definitely superior in quality to the products of methodsheretofore used inpractice.

The band of sheet-like material used to cover and mold the moist coatingin an essential step of the present process can be made of variousflexible materials that may be obtained with a very smooth surface freeof numerous minute surface irregularities which would destroy itspolish. Contrary to normal expectations, I have found that a flexibleband of this type does not permanently adhere to a coating of moistlacquer or varnish nor mar the surface characteristics of the driedcoating when the band is separated therefrom. Although there is adhesionbetween the band and the coating while the coating material is stillmoist, the coated strip and the band may be separated without difficultyafter the coating has dried. This is the case even though the band becomposed of material having a composition closely similar to that of theliquid coating material, and in practice I find it preferable to use anelongated strip of preformed cellulose acetate foil as the smoothflexible band when employing the improved method for the production ofcellulose acetate coatings on paper. Another material which is suitablefor this purpose is a band of flexible sheet metal foil having a highlypolished surface.

In another. embodiment of the invention I employ a the covering band ofsheet-like material an elongated strip of moisture-proof celluloseacetate or of wax glassine or similar flexible material having apolished wax coating. This type of material is particularly suitablebecause of its freedom from any tendency to adhere strongly to theapplied coating, even when used in the improved method together withcellulosic coating substances having a relatively high content ofsolvent. When employing such material heat is not used to hasten dryingof the combined strips, but instead either the applied coating ispermitted to dry without heating or a partial drying is' effected beforethe covering band is applied to the moist coating. In the latter event,heating means such as a hood is preferably used to heat the uncoatedface of the paper after the liquid coating is applied and before thecovering band of flexible polished material is pressed against the stillmoist coating.

In still another embodiment of the invention I provide coated paper andthe like with embossed or engraved indicia or designs in the coating byusing a flexible band of sheet-like material which itself is engraved orembossed as desired. The pItSSYll? togeth r of such a band and thecoated strip of paper in accordance with my method molds the design ofthe flexible band into the still moist coating on the strip. The moldedcoating is then dried while in contact with the band. In this way adecorated product is obtained without altering the procedure used inproducing a plain coating and without entailing additional operations.No difficulty is experienced in separating the covering flexible bandfrom the dry coated strip when following the improved method accordingto this embodiment of the invention.

One of the important advantages of my invention is that the applicationof the liquid coating material may be carried out simply and withoutundue precautions of the kind heretofore found necessary to ensure thatthe coated paper leaving the applying means be in a condition suitablefor final use. It has been customary in the application of liquidcoating materials prior to my invention to revolve the periphery of theapplying roller at a speed different from the speed of the paper, inorder to spread the coating material properly on the strip. This andother practices of like intent are made unnecessary by my invention, andthe application of the liquid coating material according to the improvedmethod may take place in the simplest way adapted to apply the desiredquantity of material fairly uniformly on the paper. Furthermore, thetendency of this customary practice to smear inks and coloring matter onthe paper being coated may be avoided entirely, since the peripheralspeed of the applying roller may be the same as the linear speed of thepaper.

Another important feature of my invention is that the practice ofpressing a flexible band of cellulose acetate foil or the like on thestill moist coating on strips of paper and of maintaining the foil as sopressed until the coating has set overcomes to a large extent theabsorption of solids from the coating solution by the paper during thedrying period. In usual coating practice, a large proportion of thesolids in the coating solution are absorbed in the paper duringabsorption and evaporation of solids so that a film coating evenapproximately comparable to laminated products cannot be obtainedwithout applying a plurality of coatings, which is commerciallyimpractical. According to my invention, however, the cellulose acetatefoil is applied and pressed on to the moist coating before thisabsorption of solids can take place and adhesion between the coating andfoil while the former remains moist holds the solids on the face of thepaper and causes the formation of a dry coating film which is hardlydistinguishable from a laminated film.

Another important advantage of the improved method is that the freshlyapplied coating is completely protected by the overlying flexible banduntil after the coating has dried and become thoroughly resistant tosurface contamina tion.

My method is further advantageous in that the drying of the coating maybe carried out in various ways and over any desired period of timewithout affecting the quality of the product to the slighest extent andwithout complicating the apparatus used in performing the method. If anextended drying period is practicable the point of separation of thecovering band from the strip of coated paper may be located farther fromthe po int of applying the liquid coating, or the rate of movement ofthe band and strip may be reduced. If rapid drying or the use of a smallplant space is important a drying chamber of any desired action may beinterposed between these two points. If it is desired to dispense withspecial drying facilities and also to conserve plant space the coatedstrip of paper and the covering band may be wound together on a suitablereel and set aside until the coating has become thoroughly dry,whereupon it is necessary only to unwind the combined materials andstrip off the covering band.

Regardless of the particular practice employed to dry the coating, thedry coated product possesses a uniform high polish throughout itslength. The flexible band used as the molding element for producingthese desirable surface characteristics is separated from the dry coatedstrip in substantially as good condition as when first used, and it maybe reused in the same manner over and over again until it becomesunsatisfactory due to accumulation of material on its smooth surface orfor other reasons. When a sheet of cellulose acetate is used as theflexible band it may be discarded after it becomes unsatisfactory, at nosubstantial loss. When a band of more expensive material, such as thinsheet metal, is used it may be more desirable to recondition the surfaceof the band by removing accumulations that may have taken place. Ineither event, however, the reconditioning of a band or the replacementof an old one may be carried out without interrupting the coatingoperations, since several bands of flexible material are usually keptavailable to be fed into contactwlth strip material leaving the coatingapplying means.

The operation of the improved method and suitable apparatus for carryingit out are indicated in the accompanying drawing, which illustratesdiagrammatically a preferred manner of practicing the invention.

Referring to the drawing in greater detail, a strip of paper or othersimilar sheet material A to be coated is moved along a feed table II)and thence through apparatus for applying a film of liquid coatingmaterial and for completing other .operations of the method. From tableIt! the strip is fed over a coating applying roller I! by feed rollersl4 and I6. Roller l2 dips into a bath of liquid coating material, forexample a cellulose acetate solution; maintained in a suitablereceptacle it. As the roller revolves it picks up a film of the liquidcoating material and carries it to the under surface of the strip A,which preferably is moved at the same speed as the periphery of rollerI! by appropriate revolution of rollers 14 and it. In this manner thefilm of liquid coating material picked up by roller I2 is continuouslyapplied to a surface of strip A, as at B, and immediately afterapplication of the coating the strip passes beyond roller l2 incondition for the next operation. To prevent adhesion between the moistcoating B and the applying roller, suitable stripping means, such as astripper finger 20, is preferably provided adjacent the back side ofroller 12.

Shortly after the film B of coating material has been applied to stripA, the coating is covered by a smooth, polished surface of a flexibleband C of sheet like material, preferably a band of preformed celluloseacetate foil. This material is kept on a roll 22 from which it isunwound and passed over a guide 24 and brought into contact Wl h themoist coating B on themoving strip A. With the band thus properlylocated over the moist coating, the strip and band are moved to getherbetween cooperating rollers 26 and 28 for applying pressure to themoving materials and bringing the band into intimate contact with themoist coating. As the materials pass between the pressure applyingrollers the smooth polished surface on the band continuously overcomesany non-uniformities in the thickness of theapplied coating and moldsthe surface of the coating so that it conforms generally to the surfaceof the band. From the pressure applying rollers the contacted materialsare then passed onward through a drying chamber 30 having entry and exitopenings 32 and 34, respectively, in which a heated atmosphere ismaintained to hasten the drying of the moist coating. The materials thentravel onward to a point where they are continuously separated.

In the illustrated form of apparatus, means are provided to breaksuperficial adhesion between the covering band and the dried coating.Such means includes a series of staggered rollers 36, 38' and4ll,-respectively, which subject the travelling materials to abruptbending and thus break any adhesion between the coating and the band.Any number of these rollers may be used, but when three are used asillustrated the materials pass over roller 36, beneath roller 38 andover roller 40, and at the latter point they are in condition for finalseparation and separate handling. A stripper finger 42 is provided atthis point to ensure proper continuous operation. The flexible band C isthen Wound on a roll 44. The dried coated paper is received by aconveyor 46 and carried onward in condition for further processing orimmediate use.

It will be apparent that the form of apparatus used in all of the stepsof this improved method may be modified in any way without departingfrom the essence of the invention. Instead of the roller l2 other formsof applying means can be used, and the strip material to be coated canbefed to the applying means in various ways. To a like extent the pressureapplying rollers 26 and 28 can be substituted by other equivalentapparatus, as well as the drying means, the means for breaking adhesionbetween the coated strip and covering band, and the means for separatingand handling the separated materials. In the coating of a continuousstrip of paper it may be desirable to employ a roll 48 above the path ofmovement of the materials so that the dry coated paper may be wound onroll 48 while the covering band is continuously wound on roll 44. In thecoating of short strips of paper and like materialthis arrangement isobviously unsuitable, and the conveyor 46 with the stripper finger 42between it and roller 40 forms a more satisfactory arrangement.

As explained hereinabove, I prefer to practice the method of myinvention by the use of a flexible band of preformed cellulose acetatefoil. This type of material is easily obtainable with a smooth surfacewhich is free from noticeable markings or surface irregularities. Whenused in the manner described it imparts a highly desirable finish tocoatings applied as a single liquid film of cellulose acetate or similarcellulosic material. When using a cellulose acetate band that does nothave a polished wax surface in the preparation of cellulose acetatecoatings, it is preferable to employ as the coating material acellulosic solution which possesses a relatively small content ofsolvent. In this manner I have found that any tendency for the moistcoating to penetrate into the surface of the band is overcome, and aclean separation between the moving materials in the final stage of themethod is obtained.

While I have described specific procedure and apparatus for carrying outmy invention, together with some of the variations which may be made inthe form of apparatus and the manner of operation, other modificationswithin the spirit of the invention will be apparent to persons skilledin the art. I therefore desire that the invention be accorded a scopefully commensurate with the spirit of the specification and therequirements of the claims without restriction to non-essential details.

I claim:

1. The method of producing glossy-surfaced sheet material whichcomprises applying a film of cellulosic solution to a moving strip ofthe material, moving the coated strip into contact with a polishedsurface of an elongated band of flexible foil material of finite lengthtravelling at the same rate as the strip to bring said surface intocontact with the moist cellulosic film, continuously pressing the stripand foil together, drying the cellulosic film while in contact with saidsurface, and thereafter stripping the coated sheet material from saidfoil.

2. The method of producing glossy-surfaced paper which comprisescontinuously applying coatings of liquid cellulosic solution tocontinuously and successively moving strips of paper, continuouslymoving the coated strips into contact with a polished surface of anelongated band of flexible sheet-like material travelling at the samerate and in the same direction as the strips to bring said surface intointimate contact with the moist cellulosic coatings, said band being offinite length continuously pressing the strips and band together,continuously drying the cellulosic coatings while maintaining the sameas pressed in contact with said surface, and continuously stripping thedry coated paper from said band.

3. The method of producing glossy-surfaced coatings on paper and similarsheet material which comprises applying a coating of cellulose acetatesolution to a strip of the material, covering the coating while it ismoist with asmooth dry surface of a band of preformed flexiblecellulosic foil, pressing the coated material and said foil together tobring the moist coating into intimate contact with said foil surface,drying the coating while maintaining said contact, and thereafterseparating the coated material and said foil.

4. The method of producing glossy-surfaced paper which comprisescontinuously applying a coating of liquid cellulosic lacquer having arelatively low content of solvent to the paper, continuously coveringthe moist coating with a flexible strip of cellulose acetate foil andmolding the surface of the coating and holding solids therein on to theface of the paper by pressing it firmly against a smooth surface of saidcellulose acetate foil, drying the coating while in contact with saidsmooth surface and thereafter separating the dry coated paper from saidfoil.

5. Apparatus for coating sheet material, such as paper, comprising meansfor applying a coating of liquid cellulosic solution to a surface ofmoving sheet material, an elongated flexible band of foil materialhaving a polished surface, said band being of finite length, means forcontinuously bringing the moist coating and said polished surface intointimate contact and for advancing the coated material and foil togetheraway from said applying means, a drying chamber having entry and exitopenings for the sheet material and foil, means for passing the sheetmaterial and foil through said chamber, and means beyond said chamberfor separating the band from the coated material.

6. Apparatus for coating sheet material, such as paper, comprising meansfor applying a coating of liquid cellulosic solution to a surface ofmoving sheet material, an elongated flexible band of foil materialhaving a polished surface, said band being of finite length, means forcontinuously bringing the moist coating and said polished surface intointimate contact and for advancing the coated material and foil togetheraway from said applying means and through a drying zone, means beyondsaid zone for flexing said sheet material and foil to break adhesiontherebetween and means for separating the foil from the dried coatedmaterial.

'7. The method of producing glossy-surfaced coatings on paper andsimilar sheet material which comprises applying a coating of cellulosicsolution to a moving strip of the material, heating the uncoated face ofthe strip partially to dry the coating, covering the partially driedcoating while it is moist with a smooth wax surface of a band ofwax-coated flexible foil material of finite length, pressing the coatingmaterial and said foil together to bring the moist coating into intimatecontact with said surface, drying the coating while maintaining saidcontact, and thereafter separating the coated material and said foil.

8. The method of producing glossy-surfaced sheet material whichcomprises applying a film of gloss forming solution to a moving strip ofthe material, moving the coated strip into contact with a polishedsurface of an elongated band of flexible foil material of finite lengthtravelling at the same rate as the strip to bring said surface intocontact with the moist gloss forming film, continuously pressing thestrip and foil together, drying the gloss forming film while in contactwith said surface, and thereafter stripping the coated sheet materialfrom said foil.

9. The method of producing glossy-surfaced coatings on paper and similarsheet material which comprises applying a coating of gloss formingsolution to a strip of the material, covering the coating while it ismoist with a smooth dry surface of a band of preformed fiexiblecellulosic foil, pressing the coated material and said foil together tobring the moist coating into intimate contact with said foil surface,drying the coating while maintaining said contact, and thereafterseparating the coated material and said foil.

10. Apparatus for coating sheet material, such as paper, comprisingmeans for applying a coating of gloss forming solution to a surface ofmoving sheet material, an elongated flexible band of foil materialhaving a polished surface, said band being of finite length, means forcontinuously bringing the moist coating and said pol

